Hi Garyo, sorry to bother you. But a number of years ago we had to replace an inspection lid that had split because the house owner kept driving over it. We ended up using the lid as a template and fit a rodding eye into a frame, this was then put back into chamber and concreted over leaving a flush rodding eye to the floor line. Looked mint and helped the house holder. That could be an easier option for you. Hope this helps.
Thanks Johnny. The main problem is that I have a 600mm wide trench under that 300mm wall, so one way or another the current chamber needs to be ripped out.